In a vehicle powered by an internal combustion engine of a type known in the art, a particulate filter can be positioned within the vehicle exhaust system to remove particulates before the particulate matter can be exhausted into the atmosphere. Such a particulate filter can be relatively efficient at capturing and retaining microscopic particles of soot, ash, sulfates, metallic particles, and/or any other particulate matter that is commonly generated as a byproduct of the fuel combustion process. While diesel engines most commonly employ such a filter, known widely as a diesel particulate filter or DPF, certain gasoline engine designs such as direct injection or DI engines can also utilize a similar particulate filter. A highly efficient particulate filter, regardless of the fuel type, can plug relatively quickly when exposed to large amounts of particulate, thus producing an increased differential pressure across the particulate filter. To alleviate this, the particulate filter can be replaced according to a predetermined maintenance cycle, or more commonly can be regenerated to extend the life of the filter.
A particulate filter, abbreviated hereinafter as PF for simplicity, can be regenerated by burning or oxidizing the accumulated particulate matter using a catalyst. The regeneration process takes place when the temperature in the PF is elevated above a threshold of approximately 450 degrees Celsius (° C.). During PF regeneration the temperature in the exhaust gas or exhaust stream is raised to this threshold level in order to facilitate the regeneration process. One way to accomplish such a temperature rise is by utilizing an oxidation catalyst (OC) in conjunction with increased hydrocarbon loading in the flow of exhaust gas upstream of the PF.
Within the OC itself, a chemical process breaks down the increased hydrocarbons into relatively inert byproducts or compounds. For example, a typical OC can use palladium or various platinum catalysts to reduce the levels of hydrocarbons by means of a simple oxidation process. This process is exothermic in nature, which results in an increased exhaust gas temperature. A temperature sensor can be used at the outlet of the OC, and control of the outlet temperature can be accomplished by adjusting the amount or level of hydrocarbons introduced into the exhaust stream. This method of temperature control is generally sufficient when the inlet to the PF or is located directly downstream of the OC outlet. However, the same method of temperature control can be less than optimal under certain circumstances, such as when a relatively large thermal mass is present between the OC outlet and the PF inlet.